U.S. patent number 5,086,366 [Application Number 07/669,459] was granted by the patent office on 1992-02-04 for prealarm circuit breaker.
This patent grant is currently assigned to Mitsubishi Denki Kabushiki Kaisha. Invention is credited to Ichiro Arinobu, Kouji Hirotsune, Kazuhiro Ishii, Kazushi Sato.
United States Patent |
5,086,366 |
Ishii , et al. |
February 4, 1992 |
**Please see images for:
( Certificate of Correction ) ** |
Prealarm circuit breaker
Abstract
In a prealarm circuit breaker which can issue a prealarm signal
before occurrence of trip, a pair-transistor is employed in a
charging circuit of a pair of capacitors, one of which serves to
make a time delay after pickup of an overcurrent and the other of
which serves to make a time delay pickup of a current of prealarm
level.
Inventors: |
Ishii; Kazuhiro (Fukuyama,
JP), Hirotsune; Kouji (Fukuyama, JP),
Arinobu; Ichiro (Fukuyama, JP), Sato; Kazushi
(Fukuyama, JP) |
Assignee: |
Mitsubishi Denki Kabushiki
Kaisha (Tokyo, JP)
|
Family
ID: |
13249417 |
Appl.
No.: |
07/669,459 |
Filed: |
March 14, 1991 |
Foreign Application Priority Data
|
|
|
|
|
Mar 16, 1990 [JP] |
|
|
2-64138 |
|
Current U.S.
Class: |
361/94; 361/97;
340/664 |
Current CPC
Class: |
H02H
3/04 (20130101) |
Current International
Class: |
H02H
3/04 (20060101); H02H 3/02 (20060101); H02H
003/08 () |
Field of
Search: |
;361/94,97,98,28
;340/664 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: DeBoer; Todd E.
Attorney, Agent or Firm: Burns, Doane, Swecker &
Mathis
Claims
What is claimed is:
1. A prealarm circuit breaker, which has an overcurrent trip
apparatus and a prealarm apparatus for issuing a prealarm signal
before occurrence of trip, comprising:
a pair-transistor having a pair of transistors;
current detection means for making a detection voltage responding
to a current flowing through said prealarm circuit breaker;
voltage applying means for operating said pair-transistor in
response to said detection voltage;
a pair of resistors which are connected in series to said
transistors, respectively;
trip signal generation means connected in series to one of said
transistors, said trip signal generation means issuing a trip
signal with a predetermined delay time when said detection voltage
exceeds a predetermined pickup voltage for trip; and
prealarm signal generation means connected in series to the other
one of said transistors, said signal generation means issuing the
prealarm signal with a predetermined delay time when said detection
voltage exceeds a predetermined pickup voltage for prealarm.
2. A prealarm circuit breaker in accordance with claim 1,
wherein
each of said predetermined delay times is dependent on a time for
charging a capacitor through each of said transistors and each of
said resistors.
Description
FIELD OF THE INVENTION AND RELATED ART STATEMENT
1. Field of the Invention
The present invention relates to a prealarm circuit breaker which
has an overcurrent trip apparatus and a prealarm apparatus for
issuing a prealarm signal before occurrence of trip.
2. Description of the Related Art
FIG. 6 is a block diagram showing a part of a conventional prealarm
circuit breaker 105. In FIG. 6, A.C. power is supplied to a load
120 through a main contact 106 of the prealarm circuit breaker 105.
A current flowing through an internal electric line 116 in the
prealarm circuit breaker 105 is detected by an air-core coil 107
connected to the electric line 116. A current signal reproducing
circuit 108, which is connected to the air-core coil 107,
reproduces current signals in response to output signals of the
air-core coil 107. A rectifier circuit 109 rectifies the current
signals reproduced in the current signal reproducing circuit 108. A
maximum phase signal detection circuit 110 selects the maximum one
of rectified signals of respective phases. Each of a pair of peak
value detection circuits 111 and 112 converts the maximum rectified
signal into a peak value to be detected. When this peak value
exceeds a value specified by a predetermined prealarm
characteristic in the prealarm circuit 115, a prealarm is issued
from the prealarm circuit 115 to thereby light an alarm lamp (not
shown) etc. Further, when the peak value exceeds a value specified
by a predetermined long time delay trip characteristic in the long
time delay trip circuit 114, a trip signal is issued from the long
time delay trip circuit 114. The main contact 106 is thereby driven
to open itself via a trip mechanism (not shown). The
above-mentioned predetermined characteristics are set by a
characteristic setting circuit 113.
FIG. 7 is a graph showing curves of the above-mentioned
characteristics. A curve "A" represents the prealarm
characteristic, and a curve "B" represents the long time delay trip
characteristic. When an overcurrent of a current value I flows in
the prealarm circuit breaker 105, the prealarm is issured with a
delay time T.sub.p from the time of generation of overcurrent,
whereas the trip signal is issued with a delay time T.sub.L from
the same time as aforementioned.
However, as a matter of fact, two curves A and B are not always
just as the graph shows. In a current range C, it is especially
difficult to keep such a relation that the two curves A and B are
located in parallel with each other. In other words, it is
difficult to make a ratio of T.sub.L to T.sub.P constant at any
current in the current range C. Further, in some cases the curves A
and B may happen to cross with each other, thereby resulting in an
undesirable state that antecedence of the curve A to the curve B in
the time range is upset within the current range C. If the curve A
is located over (in the upper side in FIG. 7 of) the curve B, trip
action occurs before the prealarm is issued.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to offer a prealarm circuit
breaker in which a long time delay trip characteristic and a
prealarm characteristic are well matched in a time-current
characteristic in a manner such that curves of both characteristics
are substantially in parallel with each other within a
predetermined current range.
In order to achieve the above-mentioned object, the prealarm
circuit breaker of the present invention comprises:
a pair-transistor having a pair of transistors;
current detection means for making a detection voltage responding
to a current flowing through the prealarm circuit breaker;
voltage applying means for operating the pair-transistor in
response to the detection voltage;
a pair of resistors which are connected in series to the
transistors, respectively;
trip signal generation means connected in series to one of the
transistors, the trip signal generation means issuing a trip signal
with a predetermined delay time when the detection voltage exceeds
a predetermined pickup voltage for trip; and
prealarm signal generation means connected in series to the other
one of the transistors, the signal generation means issuing the
prealarm signal with a predetermined delay time when the detection
voltage exceeds a predetermined pickup voltage for prealarm.
While the novel features of the invention are set forth
particularly in the appended claims, the invention, both as to
organization and content, will be better understood and
appreciated, along with other objects and features thereof, from
the following detailed description taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a prealarm circuit breaker 5.
FIGS. 2a, 2b and 2c are combination views with each other and
constitute the same block diagram as FIG. 1.
FIG. 3 is a graph showing time-current characteristic curves of the
prealarm circuit breaker.
FIG. 4 is a circuit diagram showing a main part of the prealarm
circuit breaker of the present invention.
FIG. 5 is a circuit diagram showing a part of FIG. 4.
FIG. 6 is a block diagram showing the conventional prealarm circuit
breaker.
FIG. 7 is a graph showing time-current characteristic curves of the
conventional prealarm circuit breaker.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereafter, a preferred embodiment of the present invention is
described with reference to the accompanying drawings.
FIG. 1 is a block diagram showing the whole configuration of a
prealarm circuit breaker 5. FIGS. 2a, 2b and 2c are combination
views each showing detailed configurations of respective parts of
the block diagram as FIG. 1. An A.C. power source (not shown) and a
load 120 are electrically connected via a main contact 2 and a main
circuit conductor 1 for four phases (U,V,W,N). The main contact 2
is opened by a trip coil 3 via a trip mechanism (not shown).
Respective phase currents flowing through the main circuit
conductor 1 are extracted by four current transformers 4. Output
currents of the current transformers 4 are converted into a D.C.
voltage by means of a rectifier circuit 6. A power source circuit 7
receives this D.C. voltage and supplies a predetermined voltage to
several circuits which will be mentioned later. A solid state
switch 8 is connected in series to the trip coil 3 so that the D.C.
voltage supplied from the power source circuit 7 is applied to the
trip coil 3 through the switch 8. An alarm output circuit 9, which
receives the D.C. voltage from the power source circuit 7, issues
an alarm signal in response to a trip signal inputted through each
of diodes 41, 42 and 43. An alarm output relay 10 is closed/opened
in response to operation of the alarm output circuit 9.
Four air-core coils 11 are electromagnetically connected to the
main circuit conductor 1. A current signal reproducing circuit 12,
which is connected to the air-core coils 11, reproduces current
signals (voltage) in response to output signals of the air-core
coils 11. A grounding signal reproducing circuit 13 is connected to
the air-core coils 11 in parallel with the current signal
reproducing circuit 12. This grounding signal reproducing circuit
13 reproduces a grounding signal in response to a real grounding
current flowing through the main circuit conductor 1.
The current signals reproduced in the current signal reproducing
circuit 12 are rectified by a signal rectifier circuit 14. A
maximum phase signal selection circuit 15A selects the maximum
instantaneous value of rectified signals of respective phases. A
maximum phase signal selection circuit 15B selects one phase
signal, which contains the largest signal within a predetermined
time interval, from among respective phase signals. A peak value
detection circuit 16 receives the maximum rectified signal from the
maximum phase signal detection circuit 15A and converts it into a
peak value to be detected. An effective value detection circuit 17
receives the maximum rectified signal from the maximum phase signal
detection circuit 15B and converts it into an effective value
(root-mean-square value) to be detected.
A grounding trip circuit 18 issues a trip signal when the grounding
signal reproduced in the grounding signal reproducing circuit 13
exceeds a value specified by a predetermined grounding trip
characteristic stored in the grounding trip circuit 18. A long time
delay trip circuit 19 issues a trip signal when the effective
value, namely a detection voltage of the effective value detection
circuit 17, exceeds a value specified by a predetermined long time
delay trip characteristic. A short time delay trip circuit 20
issues a trip signal when the peak value detected in the peak value
detection circuit 16 exceeds a value specified by a predetermined
short time delay trip characteristic. An instantaneous trip circuit
21 issues a trip signal when the maximum rectified signal issued
from the maximum phase selection circuit 15A exceeds a value
specified by a predetermined instantaneous trip characteristic. A
grounding trip indication circuit 22 is operated by the trip signal
issued from the grounding trip circuit 18, thereby lighting an LED
22a and closing a contact 22b. A long time delay trip indication
circuit 23 is operated by the trip signal issued from the long time
delay trip circuit 19, thereby lighting an LED 23a and closing a
contact 23b. An instantaneous or short time delay trip indication
circuit 24 is operated by the trip signal issued from the short
time delay trip circuit 20 or the instantaneous trip circuit 21,
thereby lighting an LED 24a and closing a contact 24b.
A prealarm circuit 27, which is connected to the long time delay
trip circuit 19 and the effective value detection circuit 17,
issues a prealarm signal when the detection voltage of the
effective value detection circuit 17 exceeds a value specified by a
predetermined prealarm characteristic. A prealarm output circuit 28
is operated by the prealarm signal issued from the prealarm circuit
27, thereby lighting an LED 28a and closing a contact 28b. Power
source for three indication circuits 22-24 and the prealarm output
circuit 28 is supplied by an auxiliary power source circuit 29.
The above-mentioned predetermined characteristics of long time
delay, short time delay, instantaneous and prealarm are set by a
characteristic setting circuit 26. Curves of these characteristics
are shown in FIG. 3. A characteristic curve D represents the
grounding trip characteristic, and a characteristic curve A
represents the prealarm characteristic. A characteristic curve B
consists of three characteristics in response to degree of
overcurrent. That is, the long time delay trip characteristic is
located in a current range of "LTD", and the short time delay trip
characteristic is located in a current range of "STD". Further, the
instantaneous trip characteristic is located in a current range of
"INST".
In FIG. 1, an undervoltage detection circuit 25 is connected in
parallel with the power source circuit 7 in order to always monitor
an output voltage of the power source circuit 7. Output contacts
25a, 25b, 25c and 25d of the undervoltage detection circuit 25 are
connected in series to output ends of the instantaneous trip
circuit 21 (or the short time delay trip circuit 20), the long time
delay trip circuit 19, the grounding trip circuit 18 and the
prealarm circuit 27, respectively.
In the above-mentioned prealarm circuit breaker 5, when the output
voltage of the power source circuit 7 is normal, all the output
contacts 25a, 25b, 25c and 25d are closed. In this state, when the
trip signal is issued from the trip circuit 18, 19, 20 or 21, the
solid state switch 8 is closed. The trip coil 3 is thereby excited,
and the main contact 2 is opened. Thus, the prealarm circuit
breaker 5 falls in a trip state.
When the prealarm signal is issued from the prealarm circuit 27
before the trip signal is issued, the prealarm output circuit 28
lights the LED 28a and closes the contact 28b in order to inform an
operator of occurrence of prealarm state.
Next, a main part of the embodiment is described. FIG. 4 is a
circuit diagram showing internal circuits of the characteristic
setting circuit 26, the long time delay trip circuit 19 and the
prealarm circuit 27.
The characteristic setting circuit 26 includes a reference voltage
source 26a, a buffer amplifier 26b of amplification factor 1 and
variable resistors 26c, 26d, 26e. The variable resistor 26c is
provided between the reference voltage source 26a and the earth,
and a slidable terminal of the variable resistor 26c is connected
to a non-inverted terminal of the buffer amplifier 26b. An output
terminal of the buffer amplifier 26b is connected to an inverted
terminal of the same and is connected to the earth through the
variable resistor 26d. The variable resistor 26e is provided
between the reference voltage source 26a and the earth.
The long time delay trip circuit 19 includes a V/I.sup.2 converter
19a, a comparator 19b, a transistor 19c, a diode 19d, a capacitor
19e, a discharge resistor 19f, a switch 19g and a comparator 19h.
The V/I.sup.2 converter 19a further includes voltage applying means
such as a voltage converter 19a1, a pair-transistor 19a4 and
resistors 19a5 and 19a6. The voltage converter 19a1 converts the
detection voltage V into a voltage V.sup.2. The pair-transistor
19a4 consists of a pair of transistors 19a2 and 19a3. A base of the
pair-transistor 19a4 is connected to a V.sup.2 output end of the
voltage converter 19a1. The resistors 19a5 and 19a6 are provided
between emitters of the transistors 19a2, 19a3 and the power
source, respectively. The collector of the transistor 19a2 is
grounded through the collector to emitter circuit of the transistor
19c and is also grounded via the diode 19d and the capacitor 19e.
Furthermore, the collector of the transistor 19a2 is connected to
the earth via the switch 19g and the resistor 19f. A non-inverted
input terminal of the comparator 19b is impressed with the
aforementioned detection voltage V, and an inverted input terminal
of the comparator 19b is impressed with a reference voltage for
picking up the signal of long time delay trip level. This reference
voltage is supplied from the slidable terminal of the variable
resistor 26c. An output terminal of the comparator 19b is connected
to a base of the transistor 19c, thereby normally keeping the
transistor 19c on. A connection point of the diode 19d with the
capacitor 19e and a connection point of the switch 19g with the
resistor 19f are both connected to a non-inverted input terminal of
the comparator 19h. An inverted input terminal of the comparator
19h is connected to an output terminal of the reference voltage
source 26a.
The prealarm circuit 27 includes a comparator 27a, a transistor
27b, a diode 27c, a capacitor 27d, a discharge resistor 27e, a
switch 27f and a comparator 27g. The collector of the transistor
19a3 is grounded through the collector to emitter circuit of the
transistor 27b and is also grounded via the diode 27c and the
capacitor 27d. Furthermore, the collector of the transistor 19a3 is
connected to the earth via the switch 27f and the resistor 27e. A
non-inverted input terminal of the comparator 27a is impressed with
the detection voltage V, and an inverted input terminal of the
comparator 27a is impressed with a reference voltage for picking up
the signal of prealarm level. This reference voltage is supplied
from a slidable terminal of the variable resistor 26d. An output
terminal of the comparator 27a is connected to a base of the
transistor 27b, thereby normally keeping the transistor 27a on. A
connection point of the diode 27c with the capacitor 27d and a
connection point of the switch 27f with the resistor 27e are both
connected to a non-inverted input terminal of the comparator 27g.
An inverted input terminal of the comparator 27g is connected to a
slidable terminal of the variable resistor 26e.
In the above-mentioned prealarm circuit breaker, when a normal
current flows in the main circuit conductor 1, the detection
voltage V corresponding to this normal current is converted into
the voltage V.sup.2 in the voltage converter 19a1. The
pair-transistor 19a4 is thereby operated. Since the detection
voltage V is lower than the reference voltages inputted to the
respective comparators 19b and 27a, both the transistors 19c and
27b are turned on. As a result, collector currents (I.sup.2) of the
pair-transistor 19a4 flow in the transistors 19c and 27b to the
earth. Therefore, the prealarm circuit 27 generates no alarm
signal, and the long time delay trip circuit 19 generates no trip
signal.
When a large current E (FIG. 3) flows in the main circuit conductor
1 and thereby the detection voltage V corresponding to this current
exceeds the reference voltage of the comparator 27a, the transistor
27b is turned off in accordance with change of an output signal of
the comparator 27a. Therefore, the collector current (I.sup.2) of
one of the transistor 19a3 of the pair-transistor 19a4 flows in the
diode 27c and the capacitor 27d. When a charging voltage of the
capacitor 27d exceeds the reference voltage given to the comparator
27g from the variable resistor 26e, the comparator 27g issues the
prealarm signal.
When a further large current F (FIG. 3) flows in the main circuit
conductor 1 and thereby the detection voltage V corresponding to
this current exceeds the reference voltage given to the comparator
19b, the transistor 19c is turned off in accordance with change of
an output signal of the comparator 19b. Therefore, the collector
current (I.sup.2) of one of the transistor 19a2 of the
pair-transistor 19a4 flows in the diode 19d and the capacitor 19e.
When a charging voltage of the capacitor 19e exceeds the reference
voltage given to the comparator 19h, the comparator 19h issues a
trip signal.
To the contrary, when the current flowing in the main circuit
conductor 1 drops below the current F (FIG. 3) and thereby the
charging voltage of the capacitor 19e does not reach the reference
voltage of the comparator 19h, the comparator 19h does not issue
the trip signal. When the current flowing in the main circuit
conductor 1 drops below the current E (FIG. 3) and thereby the
charging voltage of the capacitor 27d drops below the reference
voltage of the comparator 27g, the comparator 27g does not issue
the prealarm signal. The charging voltages of the capacitors 19e
and 27d are discharged through the discharge resistors 19f and 27e,
respectively. At that time, both the transistors 19c and 27b have
been already on-state. When the switches 19g and 27f are closed,
the capacitors 19c and 27d are quickly discharged through the
transistors 19c and 27b, respectively. These switches 19g and 27b
are used to select a cooling simulation mode for the load 120 (FIG.
1) or cables etc.
Next, operation of the pair-transistor 19a4 is described in detail.
FIG. 5 is a circuit diagram showing only the pair-transistor 19a4
and a pair of charging circuit which have been shown in FIG. 4.
In FIG. 5, an input voltage V.sub.i of the pair-transistor 19a4,
which is dependent on the output voltage V.sup.2 of the voltage
converter 19a1, is represented as follows:
wherein
V.sub.3BE : base-emitter voltage of the transistor 19a3,
V.sub.2BE : base-emitter voltage of the transistor 19a2,
R.sub.6 : resistance of the resistor 19a6,
R.sub.5 : resistance of the resistor 19a5,
I.sub.P : collector current of the transistor 19a3, and
I.sub.L : collector current of the transistor 19a2.
Since characteristics of the transistors 19a3 and 19a2 are just
like each other, the base-emitter voltages V.sub.3BE and V.sub.2BE
are substantially equal to each other. Therefore, the following
equation is obtained from the equations (1) and (2):
Therefore, the collector current I.sub.P is represented by an
equation:
In a transient state of the charging of the capacitor 19e, a
terminal voltage V of the capacitor 19e is generally represented by
an equation:
wherein
R.sub.19 : resistance of the resistor 19f,
t: time, and
.tau.: time constant.
By solving the above-mentioned equation (4) with respect to the
time t, the following equation is obtained: ##EQU1## Herein, since
a value of (V/(I.sub.L .multidot.R.sub.19)) is generally very much
smaller than 1, the following equation is obtainable:
wherein C.sub.19 designates a capacitance of the capacitor 19e.
In the similar way, the following equations are obtained with
respect to the transient state of charging of the capacitor 27d.
That is:
wherein C.sub.27 designates a capacitance of the capacitor 27d.
Therefore, a delay time T.sub.L by when the terminal voltage of the
capacitor 19e reaches a specific voltage V.sub.L is represented by
an equation:
Also, a delay time T.sub.P by when the terminal voltage of the
capacitor 27d reaches the voltage V.sub.L is represented by an
equation:
Therefore, a ratio of T.sub.P to T.sub.L is represented as
follows:
This equation (8) can be transformed by using the equation (3) into
an equation:
This equation teaches that the ratio of time of the prealarm to the
long time delay trip is dependent on a ratio of emitter resistance
for the transistor 19a6 to the transistor 19a5 and a ratio of
capacitance of the capactors 27d and 19e. Since these ratio are
fixed and reliable, the value of T.sub.P /T.sub.L is always kept
constant. As a result, the characteristic curves 1 and 2 are in
parallel with each other within a current range C(FIG. 3).
Although the present invention has been described in terms of the
presently preferred embodiments, it is to be understood that such
disclosure is not to be interpreted as limiting. Various
alterations and modifications will no doubt become apparent to
those skilled in the art after having read the above disclosure.
Accordingly, it is intended that the appended claims be interpreted
as covering all alterations and modifications as fall within the
true spirit and scope of the invention.
* * * * *